1. Field of the Invention
The present invention concerns a brake pressure regulator for the hydraulic brake system of a vehicle, which self-adjusts as a function of load, and has a radiating field of continuous characteristic curves that are determined by loading and other parameters of the vehicle, the radii of these curves being non-linear and degressive, i.e. downwardly concave.
2. Background Art
Upon the braking of an automotive vehicle the portion of the weight of the vehicle that is shifted forward from the rear axle toward the front axle increases with increasing braking time. Optimal braking is obtained when front and rear axles utilize the same locking force for the existing road conditions and the existing speed. This is the case when both axles remain in the transition region toward locking during the entire braking process. Since over-braking of the rear axle, i.e. locking the rear wheels with the front wheels not yet locked, must be avoided because of unstable travel behavior--danger of skidding, unfavorable influence on the steering--a brake pressure regulator must be employed to ensure that the braking force on the rear axle is never greater than the ideal braking force.
Solutions have been proposed, for instance in Federal Republic of Germany OS 27 08 941, which attempt to approximate the actual braking-force distribution to the ideal in accordance with the step-up piston principle, by which the brake pressure regulator produces a main characteristic curve which includes a family of bent lines whose points of inflection are variable as a function of the load. The performance of such a regulator in actual use is far from the ideal situation mentioned above.
Another proposed braking pressure regulator, which is known from Federal Republic of Germany OS 17 80 560, operates in accordance with the balance beam principle, the effective lever lengths of balance beam which cooperates with two pistons being automatically varied as a function of the load of the vehicle. This regulator has a field of characteristic curves including a family of straight lines whose slopes are variable as a function of the load. In actual use such a regulator is even more remote from the ideal braking force distribution, because of the braking force distribution obtained.
In Federal Republic of Germany OS 32 22 614 there is shown another proposed brake pressure regulator for producing load-dependent non-linear and continuous characteristic curves. To attempt to achieve the ideal brake pressure characteristic curves, this document provides a construction having pistons axially displaceable with respect to each other, and a pressurized air or gas column which determines the characteristics of the curves. As seen in the figures in this document, the actual mechanical characteristics of the essential pistons, the seals that are required, and the frictional forces inherent therein, are not taken into consideration. One major factor which negatively impairs the function of the proposed device and is difficult to control is the polytropic exponent, which is a function of the temperature. As a result, the pre-established characteristic curve of the vehicle brake changes continuously, for instance as a passenger car travels through a mountain pass in summer, or during the course of the seasons. Furthermore, the displacement path of the air- or gas-compressing piston changes as a measure of the degree of load, which would require continuous adjustment of the pressure regulator.